The present invention relates to a device for moulding a receptacle obtained from a parison made of a plastic material, a method for moulding the receptacle and a moulding machine, in particular for stretch-blowing.
To fully understand the importance of the invention disclosed herein, it is advantageous to explain what is intended by forming receptacles by means of stretch-blowing.
As is known, a moulding machine comprises a plurality of moulding stations at which previously-heated parisons made of a plastic material arrive. Each moulding station includes a mould constituted by two half-portions or half-moulds relatively mobile with respect to one another. For example, the mould can be linear, so that the two half-moulds are mobile by translation, or can be a “crocodile” or “wallet” type, where the two half-moulds are hinged to one another at one of the two ends.
When the parison reaches the corresponding moulding station, the half-moulds come closer to one another in such a way as to enclose the parison. As well as the half-moulds there is usually also a profiling element of the bottom of the receptacle, commonly known in the sector as the “bottom”. The bottom is arranged in one of the two bases of the mould, such as to be able to be engaged by the half-moulds during a nearing movement thereof. Moulding by stretch-blowing is done by progressively introducing a stretching rod internally of the parison, as well as a nozzle suitable for blowing pressurised air internally of the parison. In particular, first the step of pre-blowing is performed, in which the parison is lengthened by bringing the stretching rod to its end run, and the nozzle injects air at a pressure of about 6-8 bar. There follows a step of full-scale blowing, during which the nozzle injects air at a pressure of about 40 bar into the parison.
In an aseptic bottling line there exists a need to sterilise the moulded receptacles before filling them, or to sterilise the parisons before moulding them.
In particular, document EP1837037, in the name of the applicant, disclosed an apparatus and a method for sterilising receptacles after the moulding step and before the filling step. However, the sterilisation of the parisons is preferable, instead of sterilising the moulded containers, as the moulded containers have a larger surface, thus requiring longer treatment times and, in the case of chemical sterilising, greater expenditure of sterilising substances (for example hydrogen peroxide or peracetic acid).
In this context, a solution is disclosed in document EP996530 in which the parisons are sterilised by means of a sterilising product, for example hydrogen peroxide, activatable by heat.
However, this solution poses the problem of eliminating chemical residues deriving from the sterilisation, and also has the effect of lengthening process times.
Further, this solution requires a guarantee of sterility of the heating unit and handling of the parisons.
A further solution, disclosed in document EP1896329, comprises displacement of the chemical sterilisation step of the parisons after the heating thereof. However, this solution too brings with it the disadvantages of the use of sterilising chemical agents.
There also exists the possibility of using radiation sources for performing the sterilisation, as described in document EP2146838. With respect to chemical sterilisation, sterilising by radiation has the advantage of reducing operating costs due to consumption of chemical agents, resolves the problem of elimination of the chemical residues, and enables eco-sustainable plants to be realised. However, the above solution includes sterilising the parisons before heating them, so the overall process times are still long. A further advantage is connected to the need to predispose suitable screening for the radiations emitted such that they do not damage the other zones of the plant and do not constitute a risk for the operators working on control and maintenance of the machines.
In this context, the technical task underlying the present invention is to provide a moulding device for a receptacle obtained by a parison made of plastic material, a moulding method and a moulding machine, which obviate the drawbacks of the above-cited prior art.